Improving the color of surfactant agglomerates by admixing a solid bleaching agent

ABSTRACT

The present invention relates to a process for manufacturing improved color surfactant agglomerates, particularly comprising methyl ester sulfonates, for use in detergent compositions, said process comprising sulfonation of methyl ester, digestion of the sulfonation product, esterification of said sulfonated product to produce an acid product and agglomeration of said acid product, characterized in that said acid product is exposed to a solid bleaching agent immediately prior to or during agglomeration of said acid product.

TECHNICAL FIELD

The invention relates to a process for producing surfactant agglomerateswith improved color by admixing a solid bleaching agent,

BACKGROUND OF THE INVENTION

The present invention involves a novel process for producing surfactantagglomerates with improved color for use in detergent compositions byadmixing a solid bleaching agent. In particular, the surfactantagglomerate produced by the process of the present invention comprisesmethyl ester sulfonates (MES) as one of the components. The productionof alkali metal salts of α-sulfofatty acid alkyl esters ("estersulfonates") by sulfonation of fatty acid methyl esters with gaseous SO₃and subsequent neutralization of the sulfonic acids formed with aqueousalkali metal hydroxides, for example with sodium hydroxide, has beenknown for some time. The end products of this process, i.e. the alkalimetal salts of the corresponding α-sulfofatty acid alkyl esters, arepredominantly used as detergents in washing and cleaning preparations.

However, all hitherto known production processes have remainedunsatisfactory either because, although light colored end productssuitable for direct use in the detergent industry can be obtained, theyields of the sulfonation step leading to those products are highlyunsatisfactory, or because although high sulfonation yields can beobtained, the color instability of the fatty acids or fatty acid estersin the sulfonation step means that dark-colored to brown-black crudeproducts unsuitable for direct use in washing and cleaning preparationsare regularly obtained. Accordingly, a sulfonation step taken to highyields normally has to be followed by bleaching of the dark α-sulfofattyacid derivatives formed in the sulfonation step to obtain light-coloredproducts suitable for use in washing and cleaning systems. Methyl estersulfonates in particular have been used in many detergent compositionsas "natural" surfactants--i.e. surfactants derived from such sources astallow, coconut and palm. These products, in particular, have been madeonly while encountering numerous problems, including the major problemthat when combining MES with inorganic powders to make MES agglomerates,such MES agglomerates are generally dark to black in color, andtherefore contain qualities unsuitable to the consumer for a detergentproduct.

Another difficulty of hitherto known processes for the production ofaqueous ester sulfonates is that, in the course of the productionprocess, the products accumulate in the form of water-containing pasteshaving high active-substance content. In particular, past attempts tocome up with an acceptably colored detergent product comprising MESyielded high viscosity pastes using other systems. However, pastes suchas these can no longer be pumped on their own; the high viscositybehavior of ester sulfonate pastes such as these always involves therisk of blockages in apparatus and pipes. Accordingly, there has longbeen a need to find production processes for such alkali metal salts ofa-sulfofatty acid alkyl esters in which the high viscosity of theproducts obtained is avoided, or lessened in the process.

A third problem often encountered with ester sulfonates and particularlyMES comprising detergents, is that addition of hypochlorite or hydrogenperoxide to the acid mixture to solve the color problem (in addition tocausing a highly viscous paste) have also tended to cause hydrolysis atthe ester in alkaline solution and formation of a disalt too hydrophilicfor general dirt/grease detergency use.

Japanese published patent application no. 84-16870 describes a processfor the production of alpha-sulfofatty acid ester salts, in whichalpha-sulfofatty acid esters formed during the sulfonation step arebleached with H₂ O₂ in the presence of a polycarboxylic acid or one ofits salts and subsequently converted by neutralization into thecorresponding alpha-sulfofatty acid esters salt. Although the saltsformed are very suitable for use as detergents in washing and cleaningpreparations, the reaction time required for the bleaching step is ofthe order of 1 hour which does not include the time required for thefollowing neutralization reaction.

U.S. Pat. No. 4,547,318 describes a process for the production ofcolor-stable, light-colored aqueous salt pastes of washing-activealpha-sulfofatty acid esters in which the dark-colored alpha-sulfofattyacid esters emanating from the sulfonation step are first prebleachedwith alkali metal hypochlorites in neutral to mildly alkaline aqueoussolution and are then fully bleached with hydrogen peroxide in the usualway in a mildly acidic aqueous solution. The bleaching process as awhole takes several hours, involves a change in the pH value of thereaction medium with all the ensuing disadvantages, and gives aqueoussalt pastes of which the active substance content is in the range offrom 20 to 60% by weight which, as described above, gives rise toproblems affecting the process due to the considerable increase inviscosity with increasing active substance content.

U.S. Pat. No. 3,142,691 describes the production of light-coloredsulfonated fatty acids and fatty acid derivatives, more particularlythrough a process for bleaching dark-colored sulfonated fatty acids andsulfonated fatty acid derivatives by treatment with oxyacids having astrong oxidizing effect, or salts or anhydrides of these oxyacids.

U.S. Pat. No. 4,874,552 describes the production of solid, substantiallyanhydrous alkali metal salts of alpha-sulfofatty acid alkyl esters bysimultaneously mixing the esters with an aqueous solution of hydrogenperoxide or an H₂ O₂ -yielding compound with a solid alkali metalcarbonate at particular temperature ranges, optionally in the presenceof aqueous alkali metal hydroxide.

The present invention seeks to provide a process for improving the colorof surfactant agglomerates, particularly MES comprising agglomerates. Itfurther seeks to provide a process which avoids the prior art two-stepprocess of bleaching and agglomeration separately, with no visibledetriment to agglomerate color with time. The present invention furtherdescribes a process which avoids the addition of water or aqueousbleaching agents or solutions comprising other bleaching agents, thusreducing the problems associated with high viscous pastes and/or foamingacid product which is often associated with the high quantity of waterin the processes of the prior art. In accomplishing this, the presentinvention seeks to provide the advantage of a process for producinghighly active particle agglomerates with decreased water content, whichthereby reduces the need for drying of the agglomerates.

SUMMARY OF THE INVENTION

The present invention relates to a process for producing improved colorsurfactant agglomerates comprising ester sulfonates, especially methylester sulfonates (MES). In currently practiced processes, manysurfactant agglomerates, such as those comprising MES, retainundesirable color properties, rendering the surfactants unsuitable foruse in the most widely used detergent products. For this reason, mostdetergents comprising MES have bleached MES granules afteresterification with an aqueous bleaching agents prior to itsneutralization.

It has now surprisingly been found that solid α-sulfofatty acid alkylester salts substantially free from water, and particularly MEScomprising agglomerates, having outstanding color values and high colorstability can be obtained by carrying out bleaching with solid bleachingagents, and preferably, neutralization (especially dry neutralization)of the dark-colored α-sulfofatty acid alkyl esters such as MES,resulting from the sulfonation step.

In the process of the present invention, by avoiding early bleaching orneutralization of the product before agglomeration of the granules, thehigh viscous paste product is avoided, and thus the present inventionalso provides the unexpected benefit of ease in formation of thecolor-acceptable product. The present invention also reduces the problemof an overly hydrated paste which increases the tendency to disaltformation.

By avoiding the addition of hypochlorite or hydrogen peroxide to theacid mixture, and the subsequent step of hydrolysis at the ester inalkaline solution and formation of a disalt, the present inventionunexpectedly reduces the problem of an overly hydrated paste. In theprocess of the invention, a preferred embodiment allows that any alkalimetal carbonates can be used either individually or in admixture as thealkali metal carbonate both in the presence and in the absence of theaqueous alkali metal hydroxide solution. However, sodium carbonate ispreferably used for the process of the invention by virtue of itsinexpensive availability.

In addition, the products formed have a high solids or active-substancecontent and are much easier to further process and use as detergents inwashing and cleaning preparations than state-of-the-art products. Alkalimetal salts of α-sulfofatty acid esters prepared from crude α-sulfofattyacid esters by neutralization and, optionally, bleaching always containa certain proportion of dialkali metal salts of the free α-sulfofattyacids. These disalts emanate partly from the alkaline hydrolysis of themixed anhydrides of α-sulfofatty acid esters and methyl sulfuric acidproportionately present in the crude sulfonation product. Anotherproportion of disalt emanates from the unwanted alkaline hydrolysis ofthe α-sulfofatty acid methyl ester at elevated temperature and at pHvalues of 9 and higher. Therefore, extreme care must be exercised duringthe execution of these steps to avoid disalt formation.

It has surprisingly been found that the alkali metal salts ofα-sulfofatty acid esters (MES agglomerates) prepared by the process ofthe present invention avoid substantial disalt problems, without anyspecial consideration.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for manufacturing improvedcolor surfactant agglomerates, particularly comprising methyl estersulfonates, for use in detergent compositions, said process comprisingsulfonation of methyl ester, digestion of the sulfonation product,esterification of said sulfonated product to produce an acid product andagglomeration of said acid product, characterized in that said acidproduct is exposed to a solid bleaching agent immediately prior to orduring agglomeration of said acid product. The agglomerates thus formedand ultimately used in detergent compositions are generally of adequateparticle size for detergent, and especially powder detergentcompositions (preferably from about 100 um to 1400 um in diameter), andexhibit good free flowing characteristics.

In such a process, it is preferred that said acid product is neutralizedsimultaneous with or subsequent to its exposure to the solid bleachingagent; it is even more preferred that said in said process said acidproduct is neutralized subsequent to its exposure to the solid bleachingagent. It is further preferred that subsequent, concurrent with, orpreferably before the formation of the MES comprising agglomerates, theacid product is neutralized by dry neutralization.

The terms used herein are those generally known to the man skilled inthe art. Some of the initial steps of the process of the presentinvention are also known to the man skilled in the art. An example ofdigestion is an α-sulphofatty acid sulphoester process by which themixture of products leaving the falling film sulphonator adjust to themaximization of the α-sulphofatty acid ester. This can be done in aholding tank at a given temperature with a residence time large enoughso that the kinetically preferred α-sulphofatty acid sulphoester slowlyrearranges to the thermodynamically preferred α-sulphofatty acid ester.Another step known to the man skilled in the art is esterification, anexample being a process by which the acid mixture after digestion iscontacted with methanol for a given residence time at a certaintemperature in order to maximize the formation of the α-sulphofatty acidester and reduce the level of disalt formation. Other steps, such asaddition of perfumes, coating agents, solubilizing agents, etc., canalso be found in common agglomeration processes. In describingcharacteristics of detergent agglomerates a man of skill in the artrecognizes that good free flowing characteristics include such qualitiesas low caking tendency, low stickiness, low angle of repose, and thelike. Percentages herein are generally by weight, unless otherwiseindicated.

Any of a number of solid bleaching agents may be utilized in the processof the present invention. Solid bleaching agents include sodiumperborates in any hydration form (monohydrate, tetrahydrate, etc.),sodium percarbonate, etc. Non limiting-examples of such solid bleachingagents include sodium perborates (monohydrate, tetrahydrate, etc.),sodium percarbonate, urea peroxide, phosphate peroxyhydrates (such assodium pyrophosphate peroxyhydrate), calcium hypochlorite, lithiumhypochlorite, chlorinated trisodium phosphate, sodium chlorite,potassium permonosulphate, sodium or potassium bisulphites, sodium orzinc dithionites, and sodium borohydride. Preferred solid bleachingagents for use in the present invention include solid bleaching agentsselected from the group consisting of perborates, percarbonates, andorganic peroxygens (peracid); more preferred being sodium or potassiumpercarbonate. It is also preferred that the solid bleaching agent of thepresent invention be in a finely divided, powder-type form. It is morepreferred that the solid bleaching agent have an average particle sizeof less than 800 μm, even more preferred less than 200 μm.

The solid bleaching agents of the present invention may be used atvarious levels and in quantities presently used to bleach detergentgranules and in conventional ratios to the acid product beforebleaching. Preferably, the solid bleaching agent is used at a levelrelated to the acid product wherein the ratio of said solid bleachingagent is between 1% to 200% of said acid product, preferably between 10%to 100% of said acid product. It has also been found that the acidproduct, at the time of exposure to the solid bleaching agent, ispreferably at a temperature of between 60° C.-90° C.

In a preferred embodiment, the process of the present inventioncomprises the steps of:

1) Contacting the acid MES with the desired amount of the solidbleaching agent in a finely divided powder form to form a mix;

2) contacting the above mix immediately with a dry neutralizing agent(or alternatively, a dry neutralizing agent, and other desirablepowders), in a suitable mixer/agglomerator;

3) manufacturing MES agglomerates with good free flowing characteristicsin the agglomerating equipment;

where suitable (improved color) finished agglomerates comprising MES areobtained.

Steps 1 and 2 could alternative be done simultaneously, thus allowingcontact between the acid MES with the bed of premixed powders in themixer/agglomerator. In this manner, adequate product is formed, butthere may be a slight decrease in color improvement over the abovedescribed method.

The agglomerates made by the process of the present invention mayinitially appear of less than desired or adequate color, but uponstorage the color continuously improves.

Accordingly, the present invention relates to a process for theproduction of methylalkali metal salts of ester sulfonate comprisingagglomerates, and particularly MES comprising agglomerates, by bleachingand, preferably neutralization of methyl ester sulfates in an apparatussuitable for the processing of products. The MES is mixed at 20° C. to120° C., preferably 60° C. to 120° C., more particularly at 60° C. to90° C., simultaneously with a solid bleaching agent or an H₂ O₂-yielding compound and with solid alkali metal carbonate, optionally inthe presence of the ratio by weight of ester to solid bleaching agentbeing from 0.5 to 25; preferably from about 1.5 to 5. The product formedis a particle (agglomerate) of adequate characteristics to be dry addedto granular detergents and the solids formed are blended by knownmethods.

Any apparatus, planta or units suitable for the processing of MES can beused for carrying out the process according to the invention. Suitableapparatus includes, for example, falling film sulphonating reactors,digestion tanks, esterification rectors, etc. For mixing/agglomerationany of a number of mixers/agglomerators can be used. In one preferredembodiment, the process of the invention is continuously carried out.Especially preferred are mixers of the Fukae® FS-G series manufacturedby Fukae Powtech Kogyo Co., Japan; this apparatus is essentially in theform of a bowl-shaped vessel accessible via a top port, provided nearits base with a stirrer having a substantially vertical axis, and acutter positioned on a side wall. The stirrer and cutter may be operatedindependently of one another and at separately variable speeds. Thevessel can be fitted with a cooling jacket or, if necessary, a cryogenicunit.

Other similar mixers found to be suitable for use in the process of theinvention include Diosna® V series ex Dierks & Sohne, Germany; and thePharma Matrix® ex T K Fielder Ltd., England. Other mixers believed to besuitable for use in the process of the invention are the Fuji® VG-Cseries ex Fuji Sangyo Co., Japan; and the Roto® ex Zanchetta & Co srl,Italy.

Other preferred suitable equipment can include Eirich®, series RV,manufactured by Gustau Eirich Hardheim, Germany; Lodige®, series FM forbatch mixing, series Baud KM for continuous mixing/agglomeration,manufactured by Lodige Machinenbau GmbH, Paderborn Germany; Drais® T160series, manufactured by Drais Werke GmbH, Mannheim Germany; andWinkworth® RT 25 series, manufactured by Winkworth Machinery Ltd.,Bershire, England.

The α-sulfofatty acid alkyl esters used as starting materials for theprocess emanate from the processes typically used in the prior art forthe sulfonation of fatty acid alkyl esters. Esters such as these areobtained from synthetic, semi-synthetic or natural oils and/or fatswhich may in turn originate from plants, land animals or aquaticanimals. Their fatty acid residues contain from 8 to 22 carbon atoms andpreferably from 12 to 18 carbon atoms. More preferred fatty acidresidues of the present invention contain from 16 to 18 carbon atoms.The ester group of the fatty acid alkyl esters normally contains from 1to 6 and preferably from 1 to 3 carbon atoms, the corresponding methylesters being particularly preferred.

These esters are generally formed by saponification of synthetic,semi-synthetic or natural oils and/or fats and mixtures thereof andreaction of the fatty acids formed with monohydric alcohols containingfrom 1 to 6 carbon atoms or by direct transesterification with thecorresponding alcohols, particularly methanol. The corresponding fattyacid esters are then sulfonated in known manner at elevated temperaturewith a mixture of gaseous sulfur trioxide and inert gas in a sulfonationreactor, resulting in the formation of products having a degree ofsulfonation of more than 90%, which are more or less dark in color dueto the color instability of the fatty acid alkyl esters.

In an embodiment of the process of the invention, neutral to mildlyalkaline α-sulfofatty acid alkyl ester salts ("ester sulfonates") havinga water content of less than 10% and Klett color values below 100 can beprepared by simultaneous oxidative bleaching and neutralization. Thestarting materials used are the crude products of the sulfonation offatty acid alkyl esters containing from 8 to 22 carbon atoms andpreferably from 12 to 18 carbon atoms in the fatty acid chain, i.e.,α-sulfofatty acid alkyl esters.

Bleaching is carried out with solid bleaching agents as disclosed hereinor a combination of solid bleaching agents. The neutralization may becarried out with alkali metal carbonates, particularly sodium carbonateor sodium bicarbonate or other alkaline solids such as sodium citrate,sodium silicate, etc. In the course of a preferred embodiment of thepresent invention, a preferably simultaneous bleaching and dryneutralization reaction occurs, the bleaching effect of the solidbleaching agent being surprisingly enhanced or not substantiallyaffected by the dual reactions, without the problems to a significantextent which often occur with two-step bleaching and neutralizationtreatments known from the prior art. There is thus no need for a secondalkaline bleaching treatment. Neutral to mildly alkaline solids whichmay be pelletized, granulated or flaked by methods known per se areobtained as the products of the simultaneous bleaching andneutralization reaction upon cooling of the reaction mixture to roomtemperature the products are not tacky and are readily soluble in water.

The more or less dark-colored α-sulfofatty acid alkyl esters obtainedfrom the sulfonation of fatty acid alkyl esters are used insubstantially (anhydrous) form in the process of the invention. Thestarting materials may be solid or molten, depending on the α-sulfofattyacid alkyl esters used as raw material and the particular reactiontemperature selected. The reaction temperature is normally in the rangeof from 20° C. to 120° C., preferably from 20° C. to 90° C., mostpreferably in a temperature range of from 60° C. to 90° C., beingparticularly preferred for carrying out the bleaching and, preferably,neutralization process according to the invention. At high temperatures,for example at temperatures of from 60° C. to 90° C., the α-sulfofattyacid alkyl esters used are preferably present in molten form.

Solid bleaching agent and a solid alkali metal carbonate or bicarbonateare simultaneously added in the temperature range indicated to theα-sulfofatty acid alkyl esters used as starting materials, of which--asdescribed above--the methyl esters are particularly preferred by virtueof their ready accessibility from native sources, such as tallow,coconut oil or palm kernel oil, after reaction with methanol. Solidbleaching agents having application in typical detergent formulationssuch as sodium perborates and percarbonates are preferably used inpractice. The safety precautions required for the handling ofconcentrated hydrogen peroxide solutions are known to the man of skillin the art and have to be taken here.

The agglomeration process itself is well known in the art. Numerousstandardly used powders can be of use in agglomerate formation,including, for example, carborates, zeolites, silican, and the like.

In some processes where α-sulfofatty acid alkyl esters or ester mixturesare obtained directly from the sulfonation of native fatty acid alkylesters, the esters are mixed as such with the bleach and possibly aneutralizing agent, in a suitable mixer/agglomerator. The reactionbegins spontaneously. The beginning of the reaction is reflected in thefoaming (under the effect of carbon dioxide released) and graduallightening of the mixture. In the present invention, the problem offoaming is avoided, thus simplifying the obtainment of acceptableagglomerates.

METHODS OF USING THE PROCESS OF THE INVENTION Composition Examples

The following examples illustrate some of the possible embodiments ofthe present invention, but are not intended to limit the scope of theapplication.

In the following composition examples, the agglomerates contain thefollowing particulate composition.

    ______________________________________                                        Ingredients            Percent by weight                                      ______________________________________                                        Composition 1                                                                 Methyl ester sulphuric acid (acid MES)                                                               25.0%                                                  Zeolite A              40.0%                                                  Sodium carbonate       25.0%                                                  Bleaching agent (perborate monohydrate)                                                              10.0.%                                                 Composition 2                                                                 Methyl ester sulphuric acid                                                                          25.0%                                                  Zeolite A              40.0%                                                  Bleaching agent (perborate monohydrate)                                                              10.0%                                                  Other ingredients      Balance to 100%                                        Composition 3                                                                 Methyl ester sulphuric acid                                                                          25.0%                                                  Zeolite A              30.0%                                                  Bleaching agent (perforate monohydrate)                                                              20.0%                                                  Other ingredients      Balance to 100%                                        Composition 4                                                                 Methyl ester sulphuric acid                                                                          25.0%                                                  Zeolite A               0.0%                                                  Sodium carbonate       25.0%                                                  Bleaching agent (perborate monohydrate)                                                              50.0%                                                  Composition 5                                                                 Methyl ester sulphuric acid                                                                          25.0%                                                  Zeolite A              45.0%                                                  Sodium carbonate       25.0%                                                  Bleaching agent (perborate monohydrate)                                                               5.0%                                                  Composition 6                                                                 Methyl ester sulphuric acid                                                                          25.0%                                                  Zeolite A              45.0%                                                  Bleaching agent (perborate monohydrate)                                                               5.0%                                                  Other ingredients      Balance to 100%                                        ______________________________________                                    

PROCESS EXAMPLES EXAMPLE I

Acid MES (methyl ester sulphuric acid) is heated up in a conventionaloven until it reaches 60° C. At the same time, a mixture of powders isprepared containing the solid bleaching agent (parborate monohydrate),the dry neutralizing agent (sodium carbonate) and some flowing acids(Zeolite A). The mixture of these powders is placed inside an Eirichmixer model RV02 (from Maschinenfabrik Gustav Eirich) and the equipmentis started. The acid MES is then slowly poured on the powder bed untilacceptable agglomerates are formed.

EXAMPLE 2

The methyl ester sulphuric acid is again heated up to about 60° C. in asuitable vessel (for example in a thermostated bath). The desired amountof the solid bleaching agent is then added to the acid and the mix isstirred until good dispersion is observed. This mix is then poured intothe Eirich mixer model RV02 where a mixture of the rest of the powderingredients (dry neutralizing agent, flowing aids, etc.) has beenplaced. The mixer is then operated until acceptable agglomerates areformed.

We claim:
 1. A process for making improved color surfactant agglomeratescomprising methyl ester sulfonate for use in detergent compositions,said process comprising the steps of sulfonation of methyl ester,digestion of the sulfonation product, esterification of said sulfonatedproduct to produce an acid product and agglomeration of said acidproduct, wherein said acid product is exposed to a solid bleaching agentduring agglomeration.
 2. The process according to claim 1 wherein saidsolid bleaching agent is in a finely divided powder form.
 3. A processaccording to claim 1 wherein said acid product is neutralizedsimultaneous with or subsequent to its exposure to the solid bleachingagent.
 4. A process according to claim 3 wherein said acid product isneutralized subsequent to its exposure to the solid bleaching agent. 5.A process according to claim 1 wherein said solid bleaching agent isselected from the group consisting of perborate, percarbonate, andorganic peroxygens.
 6. A process according to claim 3, 4 or 5 whereinsaid acid product is neutralized by dry neutralization.
 7. A processaccording to any one of claims 1, 3, 4, or 5 wherein the ratio of saidsolid bleaching agent is from 1% to 200% of said acid product.
 8. Aprocess according to claim 7 wherein the ratio of said solid bleachingagent is from 10% to 100% of said acid product.
 9. A process accordingto any one of claims 1, 3, 4 or 5 wherein said acid product is at atemperature of between 60° C.-90° C. at the time of its exposure to thesolid bleaching agent.
 10. A process according to claim 1 wherein saidsolid bleaching agent is selected from the group consisting of sodiumpercarbonate and potassium percarbonate.
 11. In a process for makingimproved color surfactant agglomerates containing methyl ester sulfonatesurfactant for use in detergent compositions, which process comprisesthe steps of:(i) sulfonating a methyl ester to produce a sulfonationproduct; (ii) digesting the sulfonation product, (iii) esterifying thedigested sulfonation product to produce an acid product, and (iv)agglomerating said acid product, the improvement which comprisescontacting said acid product at a temperature of between about 60° C.and 90° C. with a solid percarbonate or perborate bleaching agent whilesimultaneously or shortly thereafter dry neutralizing said acid product.